The invention relates to an apparatus for examining bodies through scanning by means of ultrasound, comprising an ultrasonic applicator with at least one row of adjacent ultrasonic transducer elements and an actuating mechanism for the purpose of actuating the transducer elements individually or in groups.
An apparatus of this type is prior art e.g. from the U.S. Pat. No. 3,881,466. The ultrasonic applicator of this apparatus comprises a row of adjacent ultrasonic elements which are actuated by means of an actuating mechanism in such a manner that successively offset groups of adjacent transducer elements are sequentially energized to produce a scanning cycle. The number of energized transducer elements in one group is of a constant equal magnitude, respectively, and the step size corresponds to the raster distance between two adjacent transducer elements, since the excitation proceeds in each instance by connecting a new transducer element while simultaneously disconnecting the first transducer element of each individual group. Due to this special type of actuating mechanism, there thus results during the ultrasonic scanning a number of lines maximally corresponding to the total number of the transducer elements of the applicator. Since the resolution capability is to be as great as possible, the line density must correspondingly also be selected to be large. In the case of a specified total length of the ultrasonic applicator, this necessitates a relatively large number of transducer elements of narrow width; i.e., corresponding to the small raster distance. However, in the case of a large number of transducer elements, there result relatively unfavorable capacitance ratios between the transducer elements and the electronic actuating switches for the elements. These unfavorable capacitance ratios bring about an increased attenuation of the received echo signals, as well as a lower signal-to-noise ratio between the through-connected and disconnected transducer elements. Due to the small raster distance of the transducer elements, in addition, the width/thickness ratio of the individual transducer elements also becomes unfavorable in the sense that increased stray cross-couplings result. On the one hand, this leads to crosstalk between adjacent transducer elements, and, in addition, it leads to unfavorable oscillation ratios, since the interference effect of the undesired lateral oscillation is increased as compared with the desired thickness oscillation. In addition, there are also disadvantages from a technical-manufacturing viewpoint, since, if the number of transducer elements is increased, the number of required soldering locations is correspondingly great, and there are also resulting disadvantages in the electronic outlay, since a relatively large number of transducer elements leads to a corresponding large number of electronic actuating switches, a relatively high consumption of space and a relatively great cost.